Although drug induced trance states have been around for thousands of years.., there are a number of non drug induced practices that have been around that long also.
Ritual practices that involve people going into trance states usually have a few things in common.
There are really three main ways to induce a trance or altered state during a ritual or ceremonial event without chemical intervention.
There is sensory deprivation or sensory overload or a repetitive pattern to be followed or a combination of the last two.
Sensory deprivation may involve perfect silence and darkness and sensory overload may involve dancing, chanting and drumming.
Interesting to note is that the more modern understanding of the Ganzfeld effect is an example of this sensory deprivation or overload too. This effect most often happens when a person is in a specially made space with absolutely no sound or light. Typically in such an environment a person will start to hallucinate after a short period of time as the brain tries to construct a reality out of nothing. The brain is not used to no stimulation.
The drumming common in ceremonies like shamans have done for thousands of years will often also act as a pattern to be followed.
This type of repeating pattern of drumming sound takes advantage of the brains frequency following response where an external stimulation by repetition causes the brainwaves (neural electrical impulses) to entrain to the stimulation and then follow it if it changes slowly over time.
Often referred to as brainwave entrainment, this effect typically for drumming is about 180 bpm which in brainwave terms is 3Hz.
3Hz is in the Delta range of frequencies and is associated with sleep or very deep trance.
Often common in these ceremonies also, is a central camp fire that people dance around. This provides not only more stimulation to add to the overload but also another potential type of visual entrainment. The dancing and flickering of the flames combined with people moving in and out of the line of sight of them provide a dark/light contrast patterning that again encourages a response by the brain to match the tempo and speed of these signals.
Combine all this with belief, art and myth for example and traditional healing practices become more explainable as to why they work for the people who practice them.
Hypnotic trance practices outside of what we consider shamanic ritual have been observed in such ancient cultures as Egypt, Greece and China also.
And with just a little imagination you can start to see the comparisons of this ancient practice of altered states, symbolism and words with modern psychotherapy practices.
Inducing trance with these and other methods is as old as civilisation itself.
And today the tradition continues with raves where trance type music and flashing lights fill the room.
Modern uses of light and sound now include light machines and Audio Visual brainwave entrainment devices that can quickly and effectively cause trance states like these.